220 kV unified power flow controller（UPFC）project in Nanjing western power system

as the first one based on modular multi-level converter（MMC）technology in the world

was completely constructed and put into operation in December 2015.In this paper

the operation status of the project in 2016 and its role in the grid are introduced firstly.Then

such problem as insufficient transmission/receiving capacities at different operation modes during the development of the grid in the south part of Suzhou

limit of dynamic reactive power support ability and power supply deficiency during bipolar latching in the nearby directcurrent substation are described specifically.The feasibility

necessity and inevitability in improving power transmission and stability by the use of 500 kV UPFC in the rid of south Suzhou is introduced by way of comparison with conventional measures.The 500 kV UPFC project

on the contract to that of 220 kV

not only improves the voltage class

but also proposed creatively switchable main wiring mode of UPFC.The application of 500 kV UPFC can significantly improve the power transmission/receiving capability in South grid of Suzhou significantly

and develops remarkable safety

economic and social efficiency.