Modified unified power flow controller for medium voltage distribution networks

A conventional unified power flow controllers (UPFCs) can provide power flow control and voltage regulation in medium voltage (MV) distribution networks using partially rated converters. However, one of the main challenges of using the conventional UPFC is the unique design of the series interfacing transformer. This paper investigates a modified topology of a UPFC suitable for MV distribution networks. The modified UPFC does not need an interfacing series transformer. Hence, it offers a smaller size, lighter weight, and less cost than the conventional UPFC. It consists of single-phase back-to-back series and shunt voltage source converters. The series converters are connected to a distribution network without a series transformer, while the shunt converters are interfaced using a three-phase shunt transformer. The power ratings of the series and shunt converters were investigated considering a distribution network with a low X/R ratio. The modified UPFC was modelled in MATLAB Simulink and was connected to a two-busbar distribution network and the enhanced IEEE 33-bus distribution network. The results showed the ability of the modified UPFC to independently control active and reactive power in a distribution feeder by processing a fraction of the power transfer through the converters.