Control of A Modular Multilevel Cascaded Converter Based Unified Power Flow Controller

This paper presents a novel configuration of unified power flow controller (UPFC) using a three-phase modular multilevel cascaded converter (MMCC) shunt connected on one end of the transmission line. This offers control flexibility, lower cost and losses compared to the conventional UPFC. The control scheme combines the power flow regulation at the series converter side and voltage control at the shunt MMCC part. An overall DC capacitor voltage balancing scheme is implemented to ensure all floating capacitors of shunt MMCC and series converter voltages can be maintained at their nominal values. Simulation studies of this MMCC-UPFC for a simple two voltage sourced power network are presented and results verifies its good performance under varying real and reactive power flow conditions.