Operation Characteristics Analysis under Single-Phase Grounding Fault and Overall Protection Scheme Design of MMC-UPFC Device

The unified power flow controller based on modular multi-level converters is the most flexible ac transmission system device and it has broad market. However, when the single-phase grounding fault occurs on the transmission line, the series converter of MMC-UPFC may be damaged due to the impact of over-voltage and short-circuit current. Combined with the existing researches, in order to make up for the research gap, this paper firstly introduces the topology structure of MMC-UPFC. Then aiming at the fault occurred on the bus line, this paper analyzes the operating condition and fault characteristics under single-phase grounding fault. The proportional parameter k is proposed and if reasonably selecting the value of k, the fault grounding current can be reduced to 0 and the faulty line can operate continuously. Secondly, aiming at the fault occurred inside, according to the structure of MMC-UPFC itself, and the different AC side structures, this paper proposed a protection scheme which is designed separately for the parallel side and series side. This paper also analyzes the coperation with other protection on the bus line. Then the overall protection configuration scheme of the device is designed, which provides a reference for the engineering project. Thirdly, a simulation model is established by using the PSCAD software. Finally, an artificial short-circuit experiment in the 220 kV Nanjing west-ring network UPFC project is used for specific analysis to verify the rationality and feasibility of the proposed scheme. © 2019, Electrical Technology Press Co. Ltd. All right reserved.