Multilevel Converters for Unified Power Flow Controller: A Performance Based Analysis

In this paper, performances of the two unified power flow controllers (UPFC) based on diode-clamped multi-level inverter (DCMLI) and flying capacitor multilevel inverter (FCMLI) have been investigated. Comparative studies of performances of the two UPFC topologies are performed when both these UPFC structures are used to control the real and reactive power flows through a transmission line. Five-level structures of both the inverters have been considered. A simple and effective flying capacitor voltage balancing scheme has been used for the FCMLI and a chopper circuit based dc capacitor voltage equalization scheme has been considered for the DCMLI. The operation of the UPFCs are illustrated with representative results from the simulation studies performed using PSCAD/EMTDC.