Installation, system-level control strategy and commissioning of the Nanjing UPFC project

The Nanjing unified power flow controller (UPFC) project, which is the world's first modular multilevel converter based UPFC (MMC-UPFC) project, has been put into operation in the Nanjing Western Power Grid by State Grid Corporation of China since December 14, 2015. The project comprises three 60 MVA converters and is applied to a 220 kV ac system. The installation of the project is reported in this paper, including the optimized structure and the layout. Besides, the UPFC systemlevel control strategy is discussed. With the proposed system-level control strategy, a key transmission section of the Nanjing Western Power Grid will be operated at the preset operating point under the normal condition. While, the power flows of the transmission lines in the transmission section can be controlled within the line loading limits under fault conditions. The commissioning test results of the Nanjing UPFC project and the proposed system-level control strategy are also presented. The waveforms recorded show that the project performs well under the normal operation condition and the fault conditions. The security of the Nanjing Western Power Grid is enhanced by the installation of the Nanjing UPFC project.